Euro-IV specifications have been introduced in different countries imposing the use of gasoline sulphur to less than 50 ppm. Fluid Catalytic Cracking (FCC) unit contributes about 80-90% of the total pool of gasoline in refinery, therefore sulphur levels in this need to be decreased significantly. Refiners adopt different strategies to meet Euro IV regulations. Excess sulphur compounds in gasoline increase SOx emissions in combustion gases, reduce the activity of catalytic converter, attached to transportation vehicles and also promote corrosion of engine parts. It has been claimed that reducing sulphur content in gasoline to 50 ppm or less can improve the effectiveness of catalytic converters in reducing NOx, CO, and unburned hydrocarbons. Various methods for gasoline sulphur reduction are practiced such as
Hydro treatment of FCC feed or full-range FCC gasoline.
Undercutting FCC gasoline
Adjusting reactor and regenerator conditions
Selection of low-sulphur feeds
Increasing catalyst-to-oil ratios
Use of catalysts with higher hydrogen transfer activity (rare earth exchanged)
Use of gasoline sulphur reduction additives.
Refiners have to choose between capital investment route of hydrotreating FCC feed or gasoline or lower the gasoline end-point and incur yield loss. However, in this process high octane gasoline is converted into poor quality diesel. Technological advances in catalysts provide better solution to reduce sulphur and emission levels. Use of additives provides less expensive flexible solution to significantly reduce gasoline sulphur without affecting yield or operational constraints. In the catalytic cracking high boiling hydrocarbon fractions are converted into lighter products during the cracking reactions coke is deposited onto the catalyst which is regenerated and reused for cracking.
FCC feed stocks normally contain sulphur in the form of organic sulphur compounds such as mercaptans, sulfides and thiophenes/substituted thiophenes. The products of the cracking process correspondingly tend to contain unconverted sulphur compounds even though about half of the sulphur compounds are converted to hydrogen sulfide during the cracking process. Sulphur distribution in the cracked products depends on number of factors including feed quality, catalyst type, additives used, conversion and other operating conditions. But, in any case a certain proportion of the sulphur ends up in the light or heavy gasoline fractions and passes over to the product pool. FCC gasoline is the main contributor of refinery gasoline pool and needs special attention. Various attempts have been made in this regard which have been either published or patented.
U.S. Pat. No. 7,763,164 B1 discloses a catalyst or additive for reducing FCC gasoline and diesel blend stock sulphur content. This invention describes the use of transition metal oxides of cobalt and molybdenum for minimizing sulphur compound formation in the FCC riser.
U.S. Pat. No. 7,507,686 B2 teaches use of a sulphur reduction catalyst composition which contains a metal mainly Vanadium and Cerium stabilized USY zeolite.
U.S. Pat. No. 7,476,638 B2, U.S. Pat. No. 7,347,929 B2, U.S. Pat. No. 6,852,214 B1 disclose formulation wherein addition to USY molecular sieve; ZSM-5 is used with different metal combinations.
U.S. Pat. No. 7,431,825 B2 discloses a method for gasoline sulphur reduction using hydrotalcite and mixed metal oxide catalysts.
U.S. Pat. No. 6,692,635 B2 discloses a process for the production of gasoline with low sulphur content that comprises a hydrogenation stage of the unsaturated sulphur containing compounds and a decomposition stage of saturated sulphur containing compounds; and optionally a preliminary stage for pre-treatment of the feedstock such as selective hydrogenation of dienes. This patent does not disclose the use of catalyst additive for catalytic cracking process.
U.S. Pat. No. 5,290,427 discloses a process for hydro treatment of gasoline that consists of in fractionating the gasoline, desulphurizing the fractions and then reacting with ZSM-5 for compensating the octane loss. This patent does not disclose the use of catalyst additive.
U.S. Pat. No. 6,635,168 B2 teaches gasoline sulphur reduction (GSR) compositions containing Y zeolite and lewis acid impregnated alumina mixtures. Lewis acid is preferably Zn and preferably around 50% of the additive mixture of Y zeolite used as GSR. This patent does not disclose the reuse of refinery discarded catalyst.
U.S. Pat. No. 6,482,315 B1 discloses gasoline sulphur reduction compositions comprising alumina with Vanadium metal. The sulphur reduction catalyst is used in the form of a separate particle additive in combination with the active catalytic cracking catalyst to process hydrocarbon feed stocks in the fluid catalytic cracking (FCC) unit to produce low-sulphur gasoline and other liquid products.
U.S. Pat. No. 6,103,105 discloses process for the reduction of sulphur content in a FCC gasoline which includes fractionation of the FCC gasoline into different fractions wherein heavier fractions are hydro treated separately and the mixture is again treated and finally reaches the required sulphur level.
Not withstanding the amount of material available in the prior art, there is a continuous need to reuse waste products and provide useful and better products in FCC. There is a need in the prior art of a sulphur reduction catalyst composition comprising better physical properties superior performance without affecting the main FCC catalyst performance.